The invention relates to an apparatus for deriving information on the spatial position of box-shaped objects from image information on said objects. Furthermore, the invention relates to a method in which the apparatus is used.
During the transport and the distribution of goods, in many cases interim storage of the goods takes place. This occurs, inter alia, when parcels are being shipped, e.g., by a postal service. For the purpose of said interim storage, parcels--as a rule box-shaped objects--are accommodated in ordered stacks, such as cage-shaped containers (roll containers) or on pallets. Eventually, parcels must also be withdrawn from the stacks in order to be able to distribute them among several destinations. When this is done manually, such is a labour-intensive and physically demanding process. Options are therefore being sought to have said process carried out by robots. For this purpose, said robots should dispose of information on the spatial position of parcels in the stack in question. The stack is ordered in the sense that the containment surfaces--the lateral surfaces, top and bottom--of the parcels are substantially horizontal and vertical rectangular surfaces, and that the edges of said surfaces run substantially parallel. Deriving spatial information on the parcels from images of the stack then boils down to distinguishing horizontal and vertical surfaces in the images and determining the transitions between said surfaces--the edges of the surfaces. A problem here is the fact that the reflection coefficient, representing the light-reflecting capacity, may vary considerably over one surface of a certain parcel. In most cases, said variation then is the result of the presence of inscriptions, labels or ornaments, but may also be caused by strongly reflecting areas, e.g., in places where adhesive tape has been applied. It is therefore not sufficient to detect abrupt light-intensity transitions in an image taken of a stack of parcels.